The present invention relates to pressure transducers and switches, and more particularly a combination assembly thereof.
In many applications, for example aircraft and helicopter installations, the measurement of pressure is of vital importance. In such examplematic installations, examples of specific cases are the engine oil pressure and hydraulics. Typically this information is conveyed to a pilot in two redundant ways. One by means of a transducer and a cockpit indicator, the second by a pressure switch and a warning lamp. In this way, even if one system fails, the pilot will have enough information to correctly ascertain the present situation.
This arrangement proved necessary due to the low reliability of the older components used in the system: namely mechanical transducers, mechanical switches, indicators, lamps, wiring, etc. Modern systems improved the reliability in a significant way. One such example is the solid state piezorezistive pressure transducer, which has a significant better reliability and accuracy than the older mechanical Bourdon type potentiometer based transducers.
However, a weak link in this chain is the mechanical pressure switch. Although possible to be replaced by a solid state piezorezistive device and suitable electronics, most installations still use mechanical devices. One major reason for this is the fact that existing wiring provides only two conductors, while a solid state pressure switch requires at least an additional one for a constant supply voltage for the electronics.
The mechanical switches have another major disadvantage in that they are costly in the long run. Although individual mechanical switches are less expensive than a solid state piezorezistive transducer, due to a high failure rate, they must be replaced significantly more often than a transducer, resulting in significant costs in materials and labor.
Accordingly it is an object of the present invention, which is described below, to provide a convenient, reliable and cost effective new solution which does not require significant changes in the wiring of the plane, eliminates the unreliable mechanical switches and the associated high cost.
An apparatus including a first output and a second output for providing a pressure indication at the first output and the second output, which includes a resistive structure including a first terminal and a second terminal, for producing a pressure signal; an electronic interface including a set of input terminals coupled to the first terminal and the second terminal of the resistive structure, and an output at which a signal indicative of said pressure is produced in response to the pressure signal; a comparator arrangement including a first terminal coupled to the output of the electronic interface, and a second terminal coupled to a source representing a threshold, for comparing the pressure signal with the threshold, and for producing a pressure indication at the first output of the apparatus; an electronic buffer including an output forming the second output of the apparatus, and an input; and, a non-switched coupling path extending from the input of the buffer to the output of the electronic interface.